The photography using silver halides has been most prevailingly employed until now since ,it is superior in photographic characteristics, e.g., photographic speed, facility of gradation control, etc., to other photographic processes such as electrophotography, diazo photography and so on. In recent years, there have been developed the arts of forming images simply and rapidly by adopting a dry process utilizing a heat-applying or like means instead of the conventional wet processes using a developing solution or the like as a processing method for forming images in photosensitive materials using silver halides.
In the above-described arts, heat developable photosensitive materials are well-known, and such materials and processes therefor are described, e.g., in Shashin Kogaku no Kiso (which means "bases of photographic engineering"), given in the volume entitled "Hi-gin-en shashin" (which means non-silver photography) on pages 242-255, published by Corona Co. (1982).
Many methods for obtaining color images through heat development have been proposed.
For instance, there has been proposed a method of forming color images by binding couplers to oxidation products of developing agents, e.g., in U.S. Pat. Nos. 3,531,286, 3,761,270 and 4,021,240, Belgian Patent 802,519, Research Disclosure (abbreviated as RD, hereinafter), pp. 31-32 (September 1975), and so on.
However, in heat developable photosensitive materials of the kind which produce color images in accordance with the above-cited method, silver halides are left even after the image formation, because such materials are of a nonfixed type. Therefore, they possess a serious defect that the white part thereof is stained gradually upon exposure to intense light or during long-range storage. In addition, it generally takes a relatively long time to complete the development in the above-cited methods and, what is worse, the obtained images suffer from a disadvantage of having high fog density and low image density.
For the purpose of obviating those defects, another method has been proposed, which comprises forming or releasing imagewise diffusible dyes by heating, and transferring these diffusible dyes into an image receiving material, which contains a mordant, with the aid of a solvent such as water or the like [as disclosed, e.g., in U.S. Pat. Nos. 4,500,626, 4,483,914, 4,503,147 and 4,559,902, JP-A-59-165054 (the term "JP-A" as used herein means an unexamined published Japanese patent application)].
In the above method, a development temperature which can be adopted is still high, and the storage stability of the photosensitive materials cannot be said to be satisfactorily high. Thereupon, still another method in which transfer of dyes are carried out through heat development in the presence of a base or a precursor thereof and a trace amount of water with the intention of promotion of development, lowering of development temperature and simplification of processing operations is disclosed, e.g., in JP-A-59-218443, JP-A-61-238056, European Patent 210,660A2, and so on.
On the other hand, many methods for forming positive color images through heat development have been proposed.
For instance, U.S. Pat. No. 4,559,290 discloses a method in which so-called DRR compounds are incorporated in a photosensitive material in the oxidized form devoid of an ability to release dyes, and reduced by a reducing agent which is introduced into the photosensitive material, optionally in the form of precursor, and remains unoxidized upon heat development which functions so as to oxidize the reducing agent or its precursor in proportion to the amount of exposed silver halide, resulting in the release of diffusible dyes. In addition, European Patent 220,746A and Kokai Giho 87-6299 (Vol. 12, No. 22) disclose heat developable color photosensitive materials which utilize compounds capable of releasing diffusible dyes by the reductive cleavage of an N--X bond (wherein X represents an oxygen, nitrogen or sulfur atom) as compounds capable of releasing diffusible dyes by a similar mechanism to above. Especially in color photosensitive materials of the type which form images through the diffusion transfer of dyes among the above-cited ones, a discrimination quality of the images depends on the extent to which generation and transfer of dyes in the white part are inhibited.
However, the white part of diffusion transfer color photosensitive materials which have been proposed up to the present cannot attain the level of that of commercially available color print materials. As a means of making an improvement in the white part, capturing surplus transferred dyes is thought of. As for the art thereof, various ideas have been proposed until now. For instance, the art of incorporating a mordant of quaternary salt type in a constituent layer of a diffusion transfer photosensitive material, or providing a diffusion transfer photosensitive material with a layer of said mordant is disclosed, e.g., in U.S. Pat. Nos. 3,939,864 and 3,958,995, RD pp. 162 (October 1977), JP-A-52-148123, JP-B-59-14738 (the term "JP-B" as used herein means an "examined Japanese patent publication"), and so on. In addition, the art of incorporating dispersions of physical and chemical adsorbents into photosensitive materials is disclosed in JP-A-2-44356.
As a result of examining and comparing various compounds having an ability to capture dyes (which are called a trapping agent, hereinafter), the present inventor has already found that quaternary ammonium salt polymers used as a mordant in conventional diffusion transfer systems have excellent ability to trap dyes. However, quaternary salt polymers condense in the presence of anionic surface active agents used as emulsifying and coating aids in the field concerned and/or a viscosity increasing agent to result in formation of coarse granules, and eventually in generation of precipitates. Such being the case, adding quaternary salt polymers as they are to a coated layer as a trapping agent has turned out to be difficult. Further, it has found that when quaternary salt polymers are incorporated as they are in photosensitive materials wherein silver halides are present, many of them exert bad influences on the development reaction of silver halides to no small extent, because they contain halide ions as counter anions. Furthermore, it has turned out that when a layer (a capturing and mordanting layer) is made up of a quaternary salt polymer alone without using any anionic coating aids with the intention of avoiding the agglutination of quaternary salt polymers, an increase in thickness is caused in photosensitive materials of the kind which form dye images through diffusion transfer, resulting in lowering of maximum density.